This is the point. White threatens to take on h6 and if Black captures on g5, a dangerous knight will go to this square.
10... b8d7  11. g3g4 Otherwise Black simply plays f7-f5. 11... e7g6 This leads to a very dangerous position for Black after Firouzja's next move. 12. h3h4 A great move by a tactical magician in his element. 12... g5h4 Black's position goes downhill very fast after this.